The present invention relates generally to flexible electronic circuit boards which carry multiple electrical components to comprise an electronic module and, in particular, the invention is directed to high component density constructions utilizing a flexible circuit board arrangement having leadless and leaded components affixed thereto in a manner which minimizes the necessary space requirements of the electronic module.
There are many instances where, due to the miniaturization and portability of an electronic device, the relative density of the electrical components contained therein places a premium on the available space. Utilization of available space becomes especially critical when both components with leads, such as crystal oscillators, integrated circuits, microprocessors, resistors, capacitors, etc., and leadless components such as chip capacitors and semiconductors, etc., are used on the same flexible electronic circuit board which will be incorporated in an electronic module.
High circuit density has been obtained in the past through the use of closely-placed discrete components or subassemblies on a circuit board construction with multiple strata or by the use of multilayer circuit board construction which will permit the close stacking of circuit boards into a common housing or frame. The introduction of leadless chip components, capable of being directly positioned on an associated circuit board through the use of automated techniques, has increased the density and complexity of the completed circuit board. Manufacturing such assemblies is expensive because of the investment in the capital equipment required to achieve the automation of such activity. Prior constructions have used a flexible printed circuit board having leaded components mounted to one side wherein the board is folded in an accordion manner to conserve space.
Portable, two-way communication equipment provides a particular advantageous application for printed circuitry in either flexible or rigid printed circuit board form. A single basic or master circuit board can be designed to retain the various required electronic components for the transmitter and receiver portions of a transceiver. A disadvantage is that the master printed circuit board, once designed and laid out, is thereby fixed operationally and not readily adaptable to meet any additional or alternative operational features. For example, in portable two-way communications equipment, optional features such as tone-coded squelch operation, automatic unit identification, digital voice privacy, etc., may comprise customer selectable options. Therefore it is desirable that these optional features be designed as separate circuit modules which can be plugged into the master circuit board on an as selected basis. Furthermore the optional modules must occupy a minimum of space to minimize the area alloted to receive same on the master circuit board.
Multilayer circuit boards have been used in an attempt to minimize the space requirements of circuit modules. Making connections to conductive paths which are internal to a multilayer printed circuit board is difficult when miniaturization of electronic circuits requires the printed circuit board to be small and its conductors very thin. This problem is particularly acute when flexible printed circuit boards are utilized. A common practice has been to connect these internal conductors by the use of plated-through holes, the interior of which are plated with a conductive metallic material, so that the electrical connections are made between layers of conductors and between components inserted into such holes.
A common disadvantage relating to all of the foregoing known prior art devices involves the relatively high cost, complexity and the quantity of piece parts which comprise the various packaging apparatus for a miniaturized circuit module.